Display devices of various electronic apparatuses, which include devices such as a liquid crystal display device, have been sophisticated from year to year. For example, as display performance of the display device, high gradation display has been required. Moreover, contents displayed on the display device have been required to be not only a still picture but also a motion picture. With such a sophisticated display device, information that is necessary for displaying is increasing.
A system for displaying includes devices such as a central processor, a display control device, and a display device. The central processor processes a variety of information, the display control device carries out display control for the display device in accordance with display data supplied from the central processor, and the display device carries out an actual display. In such a system, as information increases along with a sophistication of the display device as described above, load of image processing on the central processor increases.
In this regard, in order to reduce the load on the central processor, there is a growing tendency that a system is built up so that the display control device has a function of image processing, which was originally a function of the central processor. For example, Japanese Unexamined Patent Application No. 2000-89748 (Tokukai 2000-89748, published on Mar. 31, 2000) discloses a display system that a display control device carries out image processing for displaying an image of a portrait mode in a landscape mode. Here, the portrait mode is the mode that a longitudinal length of the image is greater than its lateral length. The landscape mode is the mode that the lateral length of the image is greater than the longitudinal length. This display system is described as follows.
FIG. 13 is a block diagram schematically showing an example of the arrangement of the above display system. As shown in FIG. 13, the display system includes a central processor 51, a liquid crystal controller 52 as a display control device, a display panel 53 as a display device. Further, the liquid crystal controller 52 is provided with an address converting section 54, a primary storage section 55, and a control section 56. Note that, it is assumed in this display system that the display panel is a liquid crystal display panel.
From the central processor 51 to the liquid crystal controller 52, outputted are a color data signal (DATA) of each pixel of with respect to an image to be displayed, a display address data signal (AD) corresponding to an address of each pixel in the display panel 53, and a control signal (CTL) representing rotation information of the image to be displayed. Among these signals, the display address data signal (AD) and the control signal (CTL) are inputted to the address converting section 54. The color data signal (DATA) is inputted to the primary storage section 55.
The display address data signal (AD) is an address signal which has a X-Y dimensional coordinate. Also, the control signal (CTL) is a signal representing, for example, such information that the image of the portrait mode is rotated by 90° to display it in the landscape mode. In accordance with the rotation information indicated by the control signal (CTL), the address converting section 54, to which these signals are inputted, converts a two dimensional address data of each pixel of the display address data signal (AD) on a one-by-one basis. Further, the address converting section 54 sends the converted address data to the primary storage section 55.
In the primary storage section 55, a process is performed for writing the color data signal (DATA) sent from the central processor 51 into the corresponding address in a memory, in accordance with the address data converted in the address converting section 54. Then, in accordance with control operation of the control section 56, data, which is stored in the primary storage section 55, of the address corresponding to each pixel of the display panel 53 is read out and outputted as an image signal (IMG) to the display panel 53. The display panel 53 drives each pixel in the liquid crystal display device in accordance with the inputted image signal (IMG) to perform display of the intended image.
In the display system shown in FIG. 13, the display address data signal (AD) is sent from the central processor 51 to the liquid crystal controller 52. As described above, the display address data signal (AD) is the address signal which has a X-Y dimensional coordinate. For example, when the display panel 53 has 120×160 of resolution, an address signal corresponding to one pixel has data totaling 15 bit, including 7 bit of X-coordinate and 8 bit of Y-coordinate.
Methods for sending such an address signal are considered to be a serial transmission and a parallel transmission. The serial transmission is a method of transmitting the above 15-bit address signal in a sequence over a single line. The parallel transmission is a method of transmitting the 15-bit address signal simultaneously over a plurality of signal lines, for example, fifteen signal lines, allocating one bit of the address signal to one signal line. In case of the serial transmission, the number of signal lines required is only one. However, in some cases of the serial transmission, for example, in case where a large amount of data must be transmitted at a high speed in displaying a motion picture, a clock frequency must be extremely increased. However, it is difficult to realize the increase in the clock frequency. Instead, the parallel transmission is therefore adopted. However, in this case, an address bus with a width of plural bits must be provided between the central processor 51 and the liquid crystal controller 52.
When the address bus with a width of plural bits is provided, both of the central processor 51 and the liquid crystal controller 52 are required to be provided with a plurality of terminals corresponding to the bits. Such a provision of the plurality of terminals causes the increase in the area of a component for the terminals. In case where a display system is applied to the apparatuses that reduction in size is required, such as portable apparatuses, increase in a mounting area is a crucial drawback.
Further, in the address bus which transmits the display address data signal (AD), each time the address signal corresponding to each pixel is transmitted, the electric potential of the signal line is switched at a high speed. Power consumption by parasitic capacitance of signal wiring of which the address bus is composed, which is not negligible, causes increase in power consumption of the whole display system. Especially, in case of application of the display system to portable apparatuses, power consumption is required to be as low as possible.
Also, as described above, the electric potential in the address bus can be switched at a high speed, so that a problem of EMI (Electro Magnetic Interference) arises.
Moreover, in the above display system, the address data corresponding to each pixel is generated by the central processor 51. That is, although an address conversion processing for rotation of the image is carried out by the liquid crystal controller 52, generation of the address data must be carried out by the central processor 51. Therefore, in case where a high speed processing such as display of a motion picture is required, load of processing on the central processor 51 becomes relatively large.
The present invention is accomplished to solve the above problem, and an object of the present invention is to provide a display controller which can reduce a mounting area and power consumption and reduce the load of a processing on the central processor which performs a processing for editing image data, a display control method, and an image display system.